A conventional structure of a secondary battery such as a fuel cell is for example as illustrated in FIG. 19.
FIG. 19 is a partially-enlarged perspective view schematically showing a structure of a fuel cell of prior art.
As shown in FIG. 19, a fuel cell 100 is composed of a positive electrode (air electrode) 102 and a negative electrode (fuel electrode) 104, and between the positive electrode 102 and the negative electrode 104, an electrolyte 106 through which ions can permeate is disposed.
The positive electrode 102 is composed of a carbon electrode 102a and a platinum catalyst 102b, as shown in FIG. 20(A) which is an enlarged view of “A” of FIG. 19. Similarly, the negative electrode 104 is composed of a carbon electrode 104a and a platinum catalyst 104b, as shown in FIG. 20(B) which is an enlarged view of “B” of FIG. 19.
The positive electrode 102 and the negative electrode 104 each have a structure through which gas permeates, and thus is configured to allow oxygen and hydrogen necessary for reaction to permeate therethrough.
Outside of the positive electrode 102, a separator for a positive electrode 108 is disposed, and on the positive electrode 102 side of the separator for the positive electrode 108, an air feeding groove 108a for feeding air to the positive electrode 102 is formed.
On the other hand, outside of the negative electrode 104, a separator for a negative electrode 110 is disposed, and on the negative electrode 104 side of the separator for a negative electrode 110, an oxygen feeding groove 110a for feeding oxygen to the negative electrode 104 is formed.
The separator for a positive electrode 108, the positive electrode 102, an electrolyte 106, the negative electrode 104 and the separator for a negative electrode 110 constitute a cell 112.
As shown in FIG. 21, a fuel cell 100 is formed by stacking a large number of cells 112 so as to have a stack structure.
Meanwhile, there is a need for a sealing material to seal between the cells 112 in order to prevent the outward leakage of the electrolytic solution contained in the electrolyte 106, of air flowing through the air feeding groove 108a of the separator for a positive electrode 108, and of oxygen flowing through the oxygen feeding groove 110a of the separator for a negative electrode 110.
As such a sealing structure, it has been proposed to dispose a sealing structure between a cell frame and a cell, as in Patent Literature 1 (JP-B-3682244).
In Patent Literature 1, on both surfaces of each of the upper and lower cell frames, inner seal grooves and outer seal grooves totaling four seal groves are formed, and to these seal grooves, a total of four sealing materials formed from an O-ring are attached. That is, to a total of eight seal grooves formed on the upper and lower cell frames, a total of eight sealing materials are attached.